In general, fine patterns which are used in display devices such as semiconductor circuit devices and LCDs (Liquid Crystal Display) are formed according to a photolithography process by using a photoresist. In connection with this, the photoresist is applied on the substrate, exposed, developed, washed, and cured to produce the fine pattern.
Even though the photolithography process is advantageous in that desired patterns are precisely obtained, there are disadvantages in that many steps are performed, various types of materials are used in order to maximize the effect of the photoresist, and a great amount of photoresist is used during processes such as a coating process.
In recent, a method for obtaining a fine pattern by using an inkjet printing process has been suggested in order to avoid the disadvantages of the photolithography process.
With respect to the production of the color filter by using the inkjet printing process, a black matrix pattern which is a light blocking part is formed by using a known photolithography process, and three types of ink having red, green, and blue colors (hereinafter, the red color is designated by R, the green color is designated by B, and the blue color is designated by B) are jetted into pixel units which are defined by the black matrix patterns used as partitions.
In connection with this, if the black matrix pattern used as the partition does not have the ink repellency in respects to the ink, the ink which is jetted into the pixel units defined by the black matrix patterns flows through the light blocking part which is the black matrix pattern from the pixel unit to the adjacent pixel unit, which may cause color mixing in respects to the same color or the different colors.
Therefore, it is required that the black matrix pattern which is used as the partition during the inkjet printing has the significantly high ink repellency in respects to the ink. On the other hand, the jetted ink is uniformly spread in the pixel units only when the surface of the substrate of the pixel units defined by the black matrix pattern has the low ink repellency in respects to the ink, which prevents light leakage due to unfilling of the pixel units and reduces steps in the pixel unit or between the pixel units.
However, if the black matrix pattern is made of a black matrix material having the high ink repellency, the ink repellency substance of the black matrix material is adsorbed on the undesired pixel unit in the course of rapidly volatilizing the ink repellency substance during the post-baking process, which enables the surface of each of the pixel units to be reformed so that the surface of each of the pixel units has the ink repellency similar to that of the surface of the black matrix.
Accordingly, even though the ink is jetted, the ink is undesirably spread in each of the pixel units to cause the unfilling and significant steps in the pixel unit or between the pixel units.
The surface tension of the black matrix pattern depending on the type of surfactant which is added to provide the ink repellency to the black matrix pattern before the plasma treatment is described in Table 1, and the surface tension of the color ink which is jetted by using the inkjet process depending on the type of surfactant is described in Table 2. FIG. 1 and Table 3 show the jetting results of different types of color ink having the different surface tensions in respects to the substrate on which the black matrix patterns having the different surface tensions are formed without the plasma treatment.
In the case of the black matrices (BM1, BM4, and BM6), black matrix pattern surfaces of which have the high surface tension in the range of 36 to 45.4 mN/m, all the pixel units can be filled only by jetting 5 drops of ink 1 having the relatively high surface tension (26.4 mN/m) and ink 2 having the relatively low surface tension (24.3 mN/m). However, an overflow is observed between the adjacent pixel units. On the other hand, in the case of the black matrices (BM2 and BM5) having the middle surface tension in the range of 29 to 30 mN/m, the pixel units are filled but an overflow occurs when 20 drops of ink 1 and ink 2 are jetted. However, in the case of the black matrices (BM3 and BM7) having the surface tension of less than 25.3 mN/m, the filling is not obtained and an overflow occurs between the adjacent pixel units even though 20 drops of ink 1 and ink 2 are jetted.
As described above, when the color ink is jetted to the pixel unit of the black matrix substrate, it is required that the black matrix pattern has predetermined ink repellency in order to prevent an overflow of ink between the adjacent pixel units. In this connection with this, if the surface tension of the black matrix pattern is very low, the pixel unit has predetermined ink repellency. For this reason, the ink does not desirably flow to corners of a lower portion of the black matrix which canes into contact with the substrate to cause the unfilling. As a result, even though the amount of jetted ink (the number of ink drops) is increased, the unfilling and an overflow occur.
In order to avoid the above-mentioned problems, after the surface tension of the surface of the black matrix pattern is reduced to increase the ink repellency, the black matrix pattern may be subjected to the plasma treatment in an O2 atmosphere to be partially hydrophilized, or the black matrix pattern having the relatively high surface tension may be subjected to the plasma treatment in a CF4 atmosphere to be made partially hydrophobic. However, in this case, since the surface of the black matrix pattern and the pixel unit are totally made hydrophilic or hydrophobic during the plasma treatment, it is difficult to increase a difference in the spreadalility or the ink repellency of ink between the surface of the black matrix pattern and the pixel unit.
Furthermore, in order to avoid the above-mentioned problems, Japanese Unexamined Patent Application Publication No. 1997-203803 discloses a method for performing surface treatment in respects to a main unit by using a ink affinity treatment agent and surface treatment in respects to a projection unit by using an ink repellency treatment agent. However, this method is problematic in that the treatment is performed by using the ink affinity treatment agent so that the ink repellency treatment agent is not affected or two treatment processes are separately performed by using the ink affinity treatment agent and the ink repellency treatment agent.
Furthermore, Korean Unexamined Patent Application Publication No. 2000-0047958 discloses a color filter which has a wettability-variable layer capable of changing the wettability. However, this method is disadvantageous in that the wettability-variable layer is separately provided in addition to a partition layer which is a light blocking part and an ink layer which is an opening part, thus complicating the production process. Additionally, Japanese Unexamined Patent Application Publication No. 2000-258622 discloses a method for pattern exposing a photosensitive layer to convert an exposed portion into a hydrophilic portion. However, in this method, it is required that an additional process is performed to form an additional photosensitive layer.